Eight nano-baskets of cone calix[4]arene-crown-3, -crown-4, -crown-5, -crown-6 were synthesized and
their binding abilities towards alkali and alkaline earth metals as well as some lanthanides were studied
using differential pulse voltammetry. The novelty of this study was investigation of those nano-basket
complexes by voltammetric behaviors of two acidic moieties in each scaffold during complexation of crown
ether ring. Their voltammetric behaviors were closely related to the complex formation by entrapment of
cation into crown ether cavity and ion-dipole interaction between cation and acidic moieties in nanobaskets.
The results revealed the selective changes in voltammetric behavior of synthesized scaffolds toward
the cations. By increasing the binding ability of macrocycle and cation, the anodic oxidation peak of
carboxylic acids was decreased. It was shown that the voltammetric traces of low energy complexes did not
affected by encapsulated cations in the coordination space of crown ether and they showed no voltammetric
behavior.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3546

Mokhtari, B.

Pourabdollah, K.

English

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 4, 04NMEEE01(4pp) (2012) 
 
 
2304-1862/2012/1(4)04NMEEE01(4) 04NMEEE01-1  2012 Sumy State University 
Voltammetric Behavior of Nano-basket Complexes 
 
B. Mokhtari*, K. Pourabdollah† 
 
Razi Chemistry Research Center (RCRC), Shahreza Branch, Islamic Azad University, Shahreza, Iran 
 
(Received 18 May 2012; revised manuscript received 01 June; published online 17 August 2012) 
 
Eight nano-baskets of cone calix[4]arene-crown-3, -crown-4, -crown-5, -crown-6 were synthesized and 
their binding abilities towards alkali and alkaline earth metals as well as some lanthanides were studied 
using differential pulse voltammetry. The novelty of this study was investigation of those nano-basket 
complexes by voltammetric behaviors of two acidic moieties in each scaffold during complexation of crown 
ether ring. Their voltammetric behaviors were closely related to the complex formation by entrapment of 
cation into crown ether cavity and ion-dipole interaction between cation and acidic moieties in nano-
baskets. The results revealed the selective changes in voltammetric behavior of synthesized scaffolds to-
ward the cations. By increasing the binding ability of macrocycle and cation, the anodic oxidation peak of 
carboxylic acids was decreased. It was shown that the voltammetric traces of low energy complexes did not 
affected by encapsulated cations in the coordination space of crown ether and they showed no voltammetric 
behavior. 
 
Keywords: Nano-baskets, Differential Pulse Voltammetry, Calixcrown, Upper Rim. 
 
 PACS number: 82.45.Cc 
 
 
                                                          
* mokhtari@iaush.ac.ir  
† pourabdollah@iaush.ac.ir  
1. INTRODUCTION 
 
Nano-baskets of calixarenes and calixcrowns are a 
versatile class of macrocycles, which have been subject 
to extensive research in development of many extract-
ants [1-5]. Functionalization of calix[4]arenes at both 
the upper rim and the lower rim has been extensively 
studied. Attaching donor atoms to the lower rim of a 
calix[4]arene can improve the binding strength of the 
parent calixarene dramatically. The two main groups of 
lower rim functionalized calix[4]arenes are ca-
lix[4]arene podands and calixarene-crown ethers [6,7]. 
Distal hydroxyl groups can be connected to give 1,3-
bridged calix[4]crowns, while connection between prox-
imal hydroxyl groups leads to 1,2-bridged ca-
lix[4]crowns. 
It is found that the 1,3-bridged calix[4]crowns ex-
hibit high binding affinity and selectivity toward alkali 
and alkaline earth metal cations [8], while the re-
searches on 1,2-bridged calix[4]crowns lag far behind. 
Combining crown ethers with calix[4]arenes increases 
the cation binding ability of the parent calixarenes, and 
control of the selectivity is obtained through modula-
tion of the crown ether size. Attachment of proton-
ionizable groups to calixcrowns can further improve 
their extraction properties because the ionized group 
not only participates in metal ion coordination, but also 
eliminates the need to transfer aqueous phase anions 
into the organic phase. Ungaro et al. [9] reported the 
first di-proton-ionizable calix[4]crown-5 in 1984 and it 
showed quite high efficiency in extraction of divalent 
cations from water into dichloromethane. Combining 
crown ethers with calix[4]arenes increases the cation 
binding ability of the parent calixarenes [10-12]. In this 
work, eight diacid proton-ionizable calixcrowns were 
synthesized including cone p-tert-butyl-25,26-
di(carboxymethoxy) calix[4]arene1,2-crown-3  (10), cone 
p-tert-butyl-25,26-di(carboxymethoxy) calix[4]arene1,2-
crown-4  (11), cone p-tert-butyl-25,26-
di(carboxymethoxy) calix[4]arene1,2-crown-5 (12), cone 
p-tert-butyl-25,26-di(carboxymethoxy) calix[4]arene1,2-
crown-6 (13), cone 25,26-di(carboxymethoxy) ca-
lix[4]arene1,2-crown-3 (23), cone 25,26-
di(carboxymethoxy) calix[4]arene1,2-crown-4 (24), cone 
25,26-di(carboxymethoxy) calix[4]arene1,2-crown-5 
(25), and cone 25,26-di(carboxymethoxy) ca-
lix[4]arene1,2-crown-6 (26). The voltammetric behavior 
of the synthesized scaffolds was determined using some 
alkali, alkaline earth, transition metals and lantha-
nides. Fig. 1 depicted the structure of eight calixcrown 
scaffolds as extractant agents. 
 
2. EXPERIMENTAL 
 
Voltammetric measurements were utilized by a Model 
660 electrochemical workstation (CH Instruments, Aus-
tin, TX, USA) with a three-electrode cell including a Pt 
wire counter electrode, a glassy carbon working electrode 
and an Ag/Ag+(0.1 M) reference electrode, separated from 
the solution by a plug. The surface of the glassy carbon 
electrode was polished using 0.3 μm alumina (Buehler, 
Lake Bluff, MN) and residual alumina particles were 
thoroughly removed by placing the working electrode in 
an ultrasonic cleaner for 20 min and was dried and 
washed with pure acetonitrile. 0.1 mM calixcrowns and 
stock solution of metal perchlorate salts with various con-
centrations were prepared using acetonitrile. 0.1 M tetra-
n-butylammonium hexa-fluorohphosphate (TBAPF6) was 
used as supporting electrolyte. 
 B. MOKHTARI , K. POURABDOLLAH PROC. NAP 1, 04NMEEE01 (2012) 
 
 
 04NMEEE01-2  
 
 
Fig. 1 – The chemical structure of eight calixcrown scaffolds were synthesized and studied 
 
3. RESULTS AND DISCUSSION 
 
The complexation of 0.1 mM compounds 10 – 13 and 
23 – 26 towards various cations (including alkali, alka-
line earth, transition metals and lanthanides) were 
investigated by cyclic voltammetry (CV) and differen-
tial pulse voltammetry (DPV) at glassy carbon elec-
trode in 0.1 M TBAPF6/acetonitrile solution. According 
to Fig. 2, CVs of host macrocycles show almost same 
voltammetric behavior which is no reduction peak and 
two anodic peaks at 0.8 and 1.4 V in scaffolds 23 – 26, 
and 0.9 and 1.3 V in scaffold 10 – 13, respectively. 
 
 
 
Fig. 2 – Cyclic voltammograms of 0.1 mM 10 – 13 and 23 – 26 
at glassy carbon working electrode. 
 
This phenomenon is related to the redox behavior of 
carboxylic acids and intramolecular H-bonding (be-
tween two of carboxylic acid groups) in 10 – 13 and 23 –
 26. Although the oxidation of carboxylic acid exhibits 
one oxidation peak with two electron and proton trans-
fer in organic solution, the formation of intramolecular 
H-bonding between two carboxylic acids in 10 – 13 and 
23 – 26 causes one proton transfer easier and the other 
more difficult, leading to oxidation peaks at a more 
positive potential and a less positive potential, respec-
tively. Oxidation behavior of two carboxylic acid groups 
in 10 – 13 and 23 – 26 implies that H-bonding to car-
boxylic acid moiety is influenced by binding to cations 
because the carboxylic acids are located around the 
crown ether moiety. 
In the rest of the experiments, DPV was used in-
stead of CV to get a better resolution of waves in the 
same condition. The voltammetric behaviors of carbox-
ylic acids in each host scaffolds were compared with 
different cations in DPV to investigate the binding 
properties of 10 – 13 and 23 – 26.  
A constant volume of 10 μL per injection of the cation 
in 0.1 M TBAPF6 was added into the cell to make 0.1 – 3.0 
equivalent of cation in the solution. DPVs were recorded 
after adding stoichiometric equivalent of cations succes-
sively to the respective electrochemical solution. DPVs of 
10 – 13 and 23 – 26 depict almost same voltammetric be-
haviors with two anodic peaks, as indicated in CV. Fig. 3 
presented the differential pulse voltammograms of 0.1 
mM 10 – 13 in the presence of 0.1 mM alkali, alkaline 
earth, transition metals and lanthanides in CH3CN. 
As depicted in the first column of Fig. 3, the macro-
cycle 10 in the presence of Na+ shows significant volt-
ammetric changes of DPV in both the peak current and 
the potential. This is due to the electrostatic interac-
tion between 10 and the cations, leading to electrostatic 
perturbation of intramolecular H-bonding by encapsu-
lation of Na+ into crown ether and two carboxylic acid 
groups. According to the second column of Fig. 3, by 
addition of one equivalent of alkali, alkaline earth, 
transition metals and lanthanides to a solution con-
taining macrocycle 11, no changes were observed in the 
peak current or potentials except for Na+ and Ba2+. 
Based upon the third column of Fig. 3, addition of one 
equivalent of K+, Na+, Pb2+ to 12 caused large decrease 
in anodic peak currents or even disappearance of the 
original second anodic peak. This behavior is related to 
the electrostatic perturbation of intramolecular H-
bonding by binding of cations into crown ether and two 
carboxylic acid groups. As presented in the fourth col-
umn of Fig. 3, by addition of one equivalent of selected 
cations to macrocycle 13, no changes were observed in 
both the peak current and the peak potentials except 
for Pb2+. 
Regarding to the role of binding site in the complex, 
the crown ether groups of 10 – 13 (and 23 – 26) act 
mainly as landing sites for cations, while the carboxylic 
acid groups constitute the redox active centers as well 
as the supporting landing sites for binding. The inclu-
sion of divalent metal ions by the crown loop (and hy-
droxyl groups of carboxylic acids) may cause de-
protonation of carboxylic acids, which makes it difficult 
to oxidize carboxylic ion to carboxy radical in the oxida-
tion process. 
 
 VOLTAMMETRIC BEHAVIOR OF NANO-BASKET COMPLEXES PROC. NAP 1, 04NMEEE01 (2012) 
 
 
 04NMEEE01-3  
 
 
Fig. 3 – Differential pulse voltammograms of 0.1 mM 10 – 13 in the presence of 0.1 mM alkali, alkaline earth, transition metals 
and lanthanides in CH3CN. 
 
The reason is contributed to the repulsion between the 
carboxy radical and the positive cations in scaffolds 10-13 
and 23-26. The peak height changes of the first oxidation 
potential of one equivalent of 10-13 and 23-26 in the pres-
ence of one equivalent of different cations are tabulated in 
Table 1. The current decreasing orders of 10 – 13 and 23 –
 26 of the first peak are Na + for scaffold 10, Na+ < Ba2+ for 
scaffold 11, Na+ < K+ < Pb2+ for scaffold 12,  Pb2+ for scaf-
fold 13, Na+ for scaffold 23, Ba2+ for scaffold 24, K+ < Ba2+ 
for scaffold 25, and Ca2+ <Pb2+ for scaffold 26 that are in 
accordance with the order of potential shifts 
(ΔEp2  Ep2* – Ep2), which are tabulated in Table 2. 
 
 
Table 1 – The changes of current ratio in the first anodic peak for complexation of 0.1 mM scaffolds 10 – 13 and 23 – 26 with the 
0.1 mM solutions of different metal perchlorate salts in CH3CN 
macrocycle Cs+ Rb+ K+ Na+ Ba2+ Sr2+ Ca2+ Mg2+ Pb2+ Co2+ Zn2+ Ni2+ Nd3+ Eu3+ Tb3+ Dy3+ 
10 0.89 0.92 0.94 0.43 0.88 0.96 0.95 0.99 0.90 0.96 0.99 0.94 0.98 0.98 0.99 0.99 
11 0.88 0.90 0.88 0.56 0.47 0.94 0.96 0.99 0.96 0.98 0.99 0.98 0.99 0.98 0.99 0.99 
12 0.92 0.92 0.41 0.48 0.92 0.89 0.90 0.96 0.37 0.88 0.86 0.92 0.94 0.95 0.98 0.98 
13 0.92 0.92 0.89 0.96 0.95 0.89 0.90 0.96 0.44 0.88 0.86 0.92 0.94 0.95 0.98 0.98 
23 0.90 0.91 0.95 0.51 0.91 0.94 0.96 0.97 0.97 0.98 0.98 0.97 0.96 0.99 0.99 0.98 
24 0.90 0.94 0.91 0.89 0.44 0.92 0.93 0.97 0.94 0.98 0.97 0.99 0.98 0.98 0.98 0.99 
25 0.89 0.93 0.42 0.91 0.39 0.88 0.89 0.98 0.88 0.89 0.94 0.96 0.97 0.99 0.99 0.98 
26 0.89 0.88 0.93 0.89 0.91 0.90 0.58 0.97 0.49 0.89 0.95 0.95 0.96 0.99 0.98 0.99 
 
Table 2 – Differences of peak potentials (mV) between free and complexed macrocycles 10-13 and 23-26 by DPV 
macrocycle Cs+ Rb+ K+ Na+ Ba2+ Sr2+ Ca2+ Mg2+ Pb2+ Co2+ Zn2+ Ni2+ Nd3+ Eu3+ Tb3+ Dy3+ 
10 15 13 10 201 11 6 8 2 12 5 1 11 2 5 3 2 
11 12 16 7 188 204 5 12 2 16 6 3 4 0 3 2 2 
12 5 9 191 165 7 18 12 6 234 14 15 9 3 1 0 4 
13 5 9 3 9 6 18 12 6 179 14 15 9 3 1 0 4 
23 13 8 6 158 11 7 6 4 5 6 2 9 6 4 4 3 
24 14 12 7 6 188 7 10 0 9 7 4 3 1 2 3 2 
25 11 5 198 6 222 14 10 8 12 8 10 10 4 2 2 3 
26 14 12 6 3 12 6 161 0 178 5 11 8 5 4 2 2 
 
  
 B. MOKHTARI , K. POURABDOLLAH PROC. NAP 1, 04NMEEE01 (2012) 
 
 
04NMEEE01-4 
Complexion behavior of 10 – 13 and 23 – 26 scaffolds 
with increasing amounts of corresponded cations was con-
tinued. Figure 4 depicted the effect of concentration of cor-
responded cations to scaffolds 10 and 23. With increasing 
the amounts of cations, the anodic peaks at 0.8 V and 1.4 V 
decreased. The peak current at 0.8 V decreased quantita-
tively by increasing the concentration of Na+, and gradually 
reached to the minimum value at around one equivalent. 
 
 
 
Fig. 4 – Differential pulse voltammograms of 0.1 mM 10 (up) 
and 23 (down) with Na+ in CH3CN  
4. CONCLUSIONS 
 
The voltammetric behavior of calix[4]crowns 10 – 13 
and 23-26 and their binding abilities toward alkali, alka-
line earth, transition metals and lanthanides were exam-
ined by differential pulse voltammetry. Compounds 12 
and 25 showed their voltammetric behavior toward K+, 
10-12 and 23 towards Na+, 11, 24 and 25 towards Ba+, 
26 towards Ca2+, and 12, 13 and 26 towards Pb2+ in 
CH3CN. This was mainly related to the presence of 
crown ether group between two proximal carboxylic 
acid moieties in the complex frameworks. Comparing of 
scaffolds 10 – 13 (tert-butyl as upper rim) with 23 – 26 
(without upper rim) revealed that such complexes are 
formed in the lower rim, and the upper rim moieties 
have no remarkable effect on the lower rim complexa-
tion with cations. 
 
AKNOWLEDGEMENTS 
 
This work was supported by Islamic Azad Universi-
ty (Shahreza branch) and Iran Nanotechnology Initia-
tive Council. 
 
 
 
 
 
 
 
 
REFERENCES 
 
 
 
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Voltammetric Behavior of Nano-basket Complexes

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Voltammetric Behavior of Nano-basket Complexes

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